let width, height, cols, rows, cellWidth, current, grid = [],stack = [],
above = 0, right = 1, bottom = 2, left = 3;

function setup(){
	width = 600;
	cellWidth = 30;
	height = width;
	cols = floor(width/cellWidth);
	rows = floor(height/cellWidth);
	frameRate(15)
	
	for( let r = 0; r < rows; r++){
		for( let c = 0; c < cols; c++){
			let cell = new Cell(c,r);
			grid.push(cell);
		}
	}
	createCanvas(width,height)
	// Make the initial cell and mark it as visited
	current = grid[0];
}

// While there are unvisited cells:
function draw(){
	background(51);
	
	// Draws the grid
	grid.forEach((cell, pos) => {
		cell.show();
	})
	current.visited = true;
	current.highlight();
	
	// Choose randomly one of the unvisited neighbours
	let next = current.checkNeighbours();
	if(next){
		//mark it as visited
		next.visited = true;
		
		// Push the current cell to the stack
		stack.push(current);
		
		// Remove the wall between the current cell and the chosen cell
		removeWalls(current, next);

		// Make the chosen cell the current cell
		current = next;
	}else if(stack.length){
		//else if stack is not empty
		current = stack.pop();
	}
}
// Return a valid index given and x and a y
function index(col, row){
	if(col < 0 || row < 0 || col > cols - 1 || row > rows - 1){
		return -1;
	}
	let index = col + ( row * cols );
	return index;
}
function Cell(col,row){
	this.col = col;
	this.row = row;
	this.w = cellWidth
	this.x = col * this.w;
	this.y = row * this.w;
	// top, right, bottom, left
	this.walls = [true,true,true,true];
	this.visited = false;
	this.show = () => {
		let x = this.x,
				y = this.y,
				w = this.w;
				
		this.plot(x,y,w);
	}	
	// draws the lines for the grid
	this.plot = (x,y,w) => {
		let	corners = [[x,y],[x+w,y],[x+w,y+w], [x,y+w]];
		stroke(255);
		corners.forEach((corner, pos) => {
			let next = pos + 1;
			if(pos == corners.length - 1){
				next = 0;
			}
			if(this.walls[pos]){
				line(corner[0], corner[1], corners[next][0],corners[next][1])
			}
		})
		
		if(this.visited){
			noStroke()
			fill(255,0,255, 100)
			rect(x,y,w,w)
		}
	}
	this.checkNeighbours = () => {
		let notVisited = [],
				neighbours = [
					grid[index(this.col, this.row - 1)],
					grid[index(this.col + 1, this.row)],
					grid[index(this.col, this.row + 1)],
					grid[index(this.col - 1, this.row)]	
				]
		neighbours.forEach( neighbour => {
			if(neighbour && !neighbour.visited){
				notVisited.push(neighbour)
			}
		})
		if(notVisited.length > 0){
			let n = floor(random(0, notVisited.length))
			return notVisited[n];
		}else{
			return null;
		}
	}
	// highlights the current cell
	this.highlight = () => {
		let x = this.x,
				y = this.y,
				w = this.w;
		noStroke();
		fill(0,0,255,100);
		rect(x,y,w,w);
	}
}

function removeWalls(a,b){
		let x = a.col - b.col;
		if( x === -1 ){
			a.walls[right] = false;
			b.walls[left] = false;
		}else if( x === 1 ){
			a.walls[left] = false;
			b.walls[right] = false;
		}
		let y = a.row - b.row;
		if( y === -1 ){
			a.walls[bottom] = false;
			b.walls[above] = false;
		}else if( y === 1 ){
			a.walls[above] = false;
			b.walls[bottom] = false;
		}
}